1. Field of the Invention
This invention relates to hydrogen-permeable probes for exposure to environments that form atomic hydrogen. The probe is normally connected to a pressure-indicating or other quantitative gas sensing device such as an ion pump. More particularly, the invention relates to hydrogen probes having a limited active area such that the active part of the probe can be positioned in a desired area of a container.
2. Brief Description of the Prior Art
The use of hydrogen-permeable probe members in conjunction with an electronic pump means for determining the amount of hydrogen permeating the probe as an indication of the corrosive activity of a hydrogen-forming environment is well known.
U.S. Pat. Nos. 3,498,900 and 3,942,546 disclose the combination of a hydrogen-permeable probe and an ion pump which provides a current reading corresponding to the amount of dissociated hydrogen permeating the hydrogen-permeable section of the probe. Those patents further disclose details regarding suitable probe materials and associated apparatus for use in conjunction with the probe and ion pump combination. The probes described in those patents include finger probes and patch probes of various materials and configurations.
A particular hydrogen probe for use in sodium-cooled nuclear reactors is described in U.S. Pat. No. 3,886,444. The probe described in that patent has a thin layer of refractory metal coated on the inner wall surface of the probe for controlling the rate of permeation of hydrogen through the tube.
Attempts have been made in the past to combine a limited active area probe section with a non-permeable section, but the resulting cell effect of the bimetallic couple in an electrolyte made this undesirable. It has also been proposed to use a limited active area probe electrically insulated from the remainder of the probe structure, but the electrical insulation gave sealing and strength problems. It has further been attempted to mask off a portion of a probe with a non-metallic coating. This has the disadvantage that the coatings can be easily damaged in use, and can be chemically deteriorated in corrosive environments.